TRIPOLI (AFP) - The Islamic State in Iraq and Syria (ISIS) group claimed responsibility Friday for car bombings in eastern Libya that killed at least 31 and wounded 40 people after security sources reported dozens dead in a triple attack.

A brief statement by an ISIS branch in Libya said two suicide bombers targeted the forces of General Khalifa Haftar in Al-Qoba "in revenge for the blood of our Muslim people in the city of Derna", an apparent reference to air strikes on the eastern militant stronghold this week.

Al-Qoba is controlled by Haftar's forces who are backed by Libya's embattled internationally recognised government.

It lies just 30km west of Derna, where air strikes were launched against militant targets on Monday in retaliation for a gruesome Islamic State group video showing the beheading of 21 Christians.

The statement was signed by the ISIS branch in the eastern Cyrenaica region and was accompanied by pictures of the purported suicide bombers identified as Bitar al-Libi and Abu Abdullah al-Jazrawi.

It said they carried out "two suicide car bombings targeting the operations room of the tyrant Haftar... killing and wounding dozens... in retaliation against the conspiring Tobruk government."

It was referring to the internationally recognised parliament which is based in the eastern city of Tobruk and which ISIS accuses of having conspired in killing Muslims in Derna.

"This is a message to anyone who is tempted to attack the soldiers of the caliphate (ISIS) or any Muslim," it added.

A local official and medics said 31 people were killed in the bombings, including five Egyptians, and 40 others wounded, revising an earlier toll of 25 dead and 30 injured.

Security sources said three simultaneous attacks targeted police headquarters in Al-Qoba, as well as the home of the speaker of the internationally recognised parliament and a petrol station.

Medics said parliament speaker Aguila Salah Issa was not at home at the time of the bombings.

They said the majority of the casualties were at the petrol station where a long queue of motorists had been waiting to fill up.

The internationally recognised parliament has been based in Libya's remote east since an Islamist-backed militia alliance seized the capital last August and installed a rival parliament and government.